The most important characteristic of a roofing composition for application to a building is its ability to prevent water from entering the building. Of secondary importance, the roofing composition should also be insulating in cool weather and heat reflecting in hot weather.
While there are other desirable characteristics that a roofing composition may have, for example, durability, the need for a good long lasting waterproofing composition, having resistance to ponding water and delamination, is of greatest importance. A commonly used material for providing waterproofing for roofs is asphalt of various kinds. The asphalt is applied to the roof as a base layer. If left unprotected, however, the asphalt degrades under ultraviolet light radiation, resulting in delamination and cracking. It has, therefore, long been recognized that it is necessary to protect base asphaltic roofing layers from ultraviolet light.
One method of supplying ultraviolet light blocking is to cover the base asphaltic layer with gravel. This is effective but the resulting roof is very heavy and prone to leakage. Another method is to cover the asphalt with an acrylic polymer based coating or layer. While the acrylic polymer can provide some ultraviolet light blocking, it has been found that it is necessary in practice to add an ultraviolet light blocking filler to the acrylic polymer to provide an adequate ultraviolet light blocking effect and to reduce cost.
One difficulty with some acrylic polymer based coatings, however, is that they have poor barrier characteristics when applied as a wet coating to a hot or cold base asphaltic layer. For this reason, mobile phases, such as oils, in the base asphaltic layer, can migrate into the acrylic polymer coating and cause discolouration, with resulting undesirable heating of the roofing material and interference with its desirable characteristics, such as adhesion to the base asphaltic layer, resistance to ponding water and ultraviolet light blocking. This problem exists for hot or cold applied base asphaltic layers, whether the asphalt is applied in melted form or as a dispersion in water, since the oil phases in both cases have high mobility. Thus, it is now common for acrylic shields to be applied only when the base asphaltic layer has cooled and weathered, perhaps as long as six weeks after initial application. This makes the roofing of the building more time consuming and expensive.
The inventor has provided a new roofing composition that in particular provides for the application of an acrylic polymer to a hot or recently applied cold asphaltic layer. The acrylic polymer is provided with barrier characteristics that resist the movement of mobile phases into the shield layer. The barrier characteristics are provided in one embodiment of the invention by ensuring that the polymer include a minor (preferably less than 5%) amount of metal complexes. The polymer should be present in an amount sufficient to ensure that it can form a continuous film on application to the base asphaltic layer. Pigment volume concentration should not exceed the level that would interfere with the barrier characteristics, with the pigment volume concentration being less than 35% .